Etching process using photosensitive materials as resists



y 1965 R. H. DOWNIE ETAL 3,185,568

ETCHING PROCESS USING PHOTUSENSITIYE MATERIALS AS RESISTS Original Filed April 5, 1956 V 2 Sheets-Sheet 1 l \H J INVENTORs ROBERT H DOWNIE ROBERT J. LA FOND W/WW HTTOE/VEY May 25,1965 I R. H. DOWNIE ETAL ETCHING PROCESS USINGPHOTOSENSITIVE MATERIALS AS RESISTS original F'i led April 5, 1956 2 Sheets-Sheet 2,

INVENTORS ROBERT H. DOWNIE ATTORNEY 3,185,568 ETCHING PROCESS USING PHOTOSENSITIVE MATERIALS ASRESISTS Robert H. Downie, N eenah, Wis., and Robert J. La. Fond, Watertown, N.Y.,assignors, by mesne, assignments, to American Can Company, New York, N.Y., a corporation of New Jersey i Continuation of application Ser. No. 576,366, Apr. 5, 1956. This application Aug. 24,1960, Ser. No. 51,719

14 Claims. (Cl. 96-37) i This application is a continuation of application Serial No.576=,366, filed April 5, 1956.

This invention relates to a machine and process for etching of curved metallic surfaces, and particularly curved printing plates of magnesium to be used for direct printing in a letterpress printing operation. By the use of this machine and this process, such operation is not only possible, but can be formed with great rapidity and convenience at a minimum of cost, and it is the principal object of this invention to so perform such operation. Other objects andadvantages of the invention will be apparent from the following description and accompanying drawings, in which FIGURE l is a perspective view, partially cut away, of a machine which in part comprises this invention, and which may be used in carrying out the process, and

FIGURE 2 is a cross-sectional view along line 2--.-2 of FIGURE 1, but showing certain elements of the machine in slightly different operating position.

Referring to the accompanying drawings, the machine includes a drum or container 30 divided into an upper portion 1 and a lower portion2, and tightly closed at its ends by conventional elements not specifically illustrated.

along one side by conventional hinge means 3 andat The two drum portions are hingedtogether an opposite side meet in a conventional joint 4. i The connection 3 and the joint 4 should be substantially liquid-tight, but permitting ready opening of the upper drum portion 1 by use of a handle 5. The lower portion 2 of the drum is fixed to a firm base, not shown, of any suitable sort.

Extending through the drum isan axle or shaft 6.

upon which a cylinder 7 is fixedly mounted within the drum. Shaft 6 is variably rotatable and may be longitudinally shiftable by fa conventional motor 8 through the gear box connection 9. It will be understood that the cut-away extension of shaft 6 is conventionally mounted in a journal permitting rotation and longitudinal shifting of the shaft.

A series of spray pipes 10 is mounted in the lower portion of the drum, at an equal distance from the center of shaft 6. Pipes 10 have nozzles 11 mounted along their length at intervals, adapted for directing a spray of liquid toward cylinder 7 quite precisely along the direction of a radius extending from the center of shaft 6. The requirement for; precise radial propulsion of the etchant preferably is met by a liquid spray constituted of a series of individual liquid streams or propulsions, each of which is individually directed substantially entireiy along the direction of a: radius extending from the center of the shaft 6. This requirement obviously would not be satisfied, however, by a series of coneshaped or fan-shaped sprays a significant part of which were directed other than radially. The essentialfeature is that the spray or propulsion of etchant liquid, whether.

applied continuously orintermittently, be directed substantially 1 entirely along the direction of radii extending from the center of shaft 6, so that undercutting is avoided as described in detail later herein. Thus, the term spray of liquid as herein utilized refers to such a series of liquid streams or series of individual liquid United States Patent "ice 3,185,568 Patented May 25, 1965 ,will be obvious from later description, a series of spray holes in pipe might. readily be substituted for the nozzles 11. The pipes 10 are closed at one end, while two alternate ones at their other end are connected to a manifold 12 and the other two to a manifold 13. The manifolds in turn are 'by means of a pipe 14 connected to a liquid pump 15 and a liquid reservoir 16. A drain line 17 serves to drain liquid from the drum into the reservoir 16.

A baifie 18 is located to each side and slightly above the mid-point of cylinder 7, being mounted on the upper portion 1 of the drum and extending in close proximity tothe surface of cylinder 7 when the drum is closed. The interior of drum is thusdivided into a lower portion below baflles 18 and an upper portion therei above. A series of spray pipes 19 and nozzles 20, similar to those previously described, are also mounted in the upper portion of the drum, and are supplied with The bafiles 18 serve to catch and drain off the principal portion of liquid sprayed from pipes 19, thus preventing the liquid from those pipes mixing with liquid sprayed from pipes 10.

A printing plate 21 is mounted around a portion of the circumference of cylinder 7 by conventional fastening means indicated at 22.

i In FIGURE 1, the plate 21 is shown in the upper portion 1 of the drum 30 where it is exposed to the action of liquid expelled from spray pipes 19 through nozzles 20, where as in FIGURE 2, the cylinder 7 is represented as rotated to a point at which the plate 21 is. within the lower section 2 of drum 30 where it is exposed to the action of the liquid expelled from spray p then acid or electrolytically etched by conventional means requiring a considerable number of repeated etching and image-protecting steps or operations. This is a time-consuming and laborious operation, and it is quite expensive. After the plate is etched, a plastic mold or pattern is made of the etched surface, and this mold is then used to make a metallic flat electrotype plate, usually of copper backed by lead, bearing the original image. This plate is then formed to the curvature necessary for it to fit onto the base printing cylinder of the letterpress printing machine and thereafter coated with a hard metal such as chromium to provide a durable printing surface.

This bending or conformation of the flat plate to a curved shape obviously leads to distortion of the image originally printed on the flat plate, and this distortion causes great difliculty in make ready of the machine for the printing operation. It requires great skill, and considerable trial and error effort, to arrange in proper register a series of these image-distorted plates when a mult-i-colored pattern is to be printed. Frequently the distortion causes such difiiculty that some of the plates have to be entirely remade, and frequently adjustment by sectioning of the plates or additional distortion of the image must be made. The result is the expenditure of much time. and effort, with almost impossibility of securing an exact register of colors in a multi-colored" desired. Exact register of the plates on the printing machine, with consequent precise register of the printed de signs in multi-colored printing operations, is easily attained. In addition, the invention permits very rapid manufacture of the printing plates, and eliminates the intermediate steps of manufacturing a first plate which is not used for printing but which is merely used for making a mold or pattern from which the printing plate is cast. The invention is further particularly useful in the manufacture of printing plates of magnesium as compared to the conventional electrotype plates, and it therefore permits a higher speed of operation of the printing machine or press since the lighter magnesium plates will not have as great a tendency to breathe due to centrifugal force when the base cylinders of the press are operated at very high speed.

When carrying out the process and operating the machine, a preformed (curved) magnesium printing plate is first coated on its outer surface with a photo-sensitive mordant or resist, such as Gaco, which is a polyvinyl alcohol acid-resist manufactured by Jones Graphic Arts Company of Toledo, Ohio. The coated surface is then exposed through a negative of the image desired to be reproduced, in the conventional manner such as is now used in the production of rotogra-vure printing cylinders, or in any other conventional fashion, and the coated surface is then developed and treated. The plate 21 is then mounted on cylinder 7, the cylinder rotated to present the plate to the lower portion of the drum, and a spray through pipes 16 is turned on to apply an etchant solution against the surface of cylinder 7 and plate 21 exposed thereto. A preferred etchant for this purpose consists of an aqueous solution of approximately by weight 10.5-12.5% nitric acid, 7% diethylbenzene, 0.4% Aerosol EG and 0.31.5 l* gelatin. Aerosol EG is a well-known solution of di-octyl sodium sulfosuccinate manufactured by American Cyanamid Company of New York, New York. The solution is used at a temperature of from about 60 F. to 90 F. and preferably at 70 F. While the etchant spray is being directed against the surface of the cylinder and plate, radially thereof, shaft 6 carrying with it cylinder 7 and plate 21 is variably rotated, and may be longitudinally shifted within the drum through the conventional erratic gear assembly 9 driven by motor 8. The movement of cylinder 7 and plate 21 is for the purpose of insuring an even exposure of the plate to the action of the etchant, to give a consistent etch to that portion of plate 21 which is not covered by the resist image.

The preferred etchant solution as noted above permits an unusually deep etch without undercutting of the printing surface covered by the resist, since the diethylbenzene component fortified by the Aerosol EG tends to build up a coating which is resistant to the etching action of the nitric acid. This coating is effective on surfaces parallel to the line of flow of the etchant, where the hydraulic force of the etchant flow is less effective to displace the film. The gelatin in the etchant solution provides a tempering effect upon the film to permit its displacement from the surface perpendicular to the etchant flow, where the flow has a hydraulic force tending to break down the film or coating.

When the etching action has proceeded to the desired depth, preferably about 0.020 to 0.040" for a magnesium plate with the preferred etchant, the drive mechanism for shaft 6 is actuated to revolve cylinder 7 to present plate 21 to the upper portion of the drum, where the plate can be washed with water from pipes 19 to remove the etchant solution, with drainage water being carried away by baffles 18. Further, in particular instances where the film built up by the etchant solution becomes excessive, as an intermediate step, cylinder 7 may be rotated to expose plate 21 to washing action in the upper portion of the drum to wash this film from the surface to be etched. In particular situations, shaft 7 may be continuously,

though reversibly, rotated, to alternately present plate 21 to the etching and washing actions, which may eliminate the necessity for the gelatin ingredient of the preferred etchant.

After the plate has been thus etched and washed, the drum may be opened and the plate removed for dissolving of the resist and for any necessary further mechanical routing of the non-printing surface of the plate. The plate is then ready for mounting on the printing press, and bears the original, undistorted image which is desired to be printed. Since the same exact-image process is used for formation of all of the plates required for the particular printing operation, a perfect register of the printing images may be conveniently obtained.

This invention is particularly advantageous when used with a method for etching magnesium plates which requires no mechanical or electrolytic routing. In this no-routing process, the magnesium plate is coated with a primary resist such as Gaco, which is exposed through a negative of the exact image it is desired to print. After the primary resist is developed and treated conventionally, a secondary resist such as KPR is coated onto the plate and exposed in exact register with the first exposure through a spread negative made from the original art work by a conventional line variator or by photographic contacts. This gives a proportional enlargement of the primary image in the secondary resist. The secondary coating is then developed and treated conventionally, to produce a secondary resist overlying the primary resist. KPR is a well-known commercial photo resist of the photosensitized resin type manufactured by the Eastman Kodak Company of Rochester, New York.

The plate is then attached to cylinder 7, rotated within the drum, and sprayed with a normal etching solution such as an aqueous solution of 540% nitric acid. This etching action can be continued until an etch approximately 0.020" in depth has been achieved, and is discontinued before the undercutting of the secondary resist has reached the boundaries of the primary resist. The plate is then removed from the drum and the secondary resist is dissolved by a solvent in which the primary resist is not soluble. The plate then may be placed in a second machine like that of FIGURE 1 for exposure to the action of the nitric acid-diethylbenzene-Aerosol EG-gelatin etchant first above described. As previously described, this permits an additional etch of approximately 0.020" depth without undercutting of the primary resist, for a total etch depth of approximately 0.040", which is sufficient to eliminate the need for further mechanical routing. By the use of two machines in this manner, a high rate of production of curved magnesium letterpress plates can be achieved.

It is readily seen that instead of using two machines as just described, the shaft 6 could be connected to gear assembly 9 by conventional quick-disconnect means. Then the just-described etching process could be carried out by using two shafts each carrying a set of plates to be etched. The first etch would be made on the first set of plates, which would be removed on the shaft for dissolution of the secondary resist while the second set was given the first etch. Then, while the second set is removed for dissolution of the secondary resist, the first shaft may be returned to the machine for application of the second etchant through pipes 10, with only an obvious modification of the machine to provide a source of the second etchant.

By increasing the number of pipes 11 and the number of spray holes or nozzles therein, any new for longitudinal shifting of shaft 6, cylinder 7 and plate 21 may be eliminated. The variable rotation of shaft 6 will alone give a sufficiently consistent exposure of the plate surface to the etchant solution, to eliminate variations in etching action on the various portions of the plate surface. The variable rotation of the shaft prevents uneven washing in and dripping of the etchant from various portions cheeses of the plate surface, thereby preventing an uneven etching action.

It will be obvious that this machine and process are admirably suited to the etching of magnesium rotogravure printing cylinders, merely by substituting for cylinder 7 the magnesium cylinder to be etched. Modification of shaft 6 to permit attachment of such a cylinder might be accomplished in any of several obvious Ways, and need not be detailed here. While the foregoing de scription has been primarily concerned with application of the invention to etching of magnesium surfaces, the invention is not to be considered as limited to such use, for it may successfully be employed in the etching of other metallic surfaces, such as zinc.

Variations from and modifications of this invention might be made in a variety of ways without departing from the spirit thereof, and it is accordingly intended that no restriction be placed thereon other than as required by the appended claims.

We claim:

1. A method for providing a curved metallic printing surface, comprising preforming a metallic surface to the desired printing surface curvature, coating the surface with a photosensitive resist, exposing the coated surface to the image to be printed, developing the coating, directing an etchant spray under positive pressure against the surface substantially radially thereof while variably rotating the surface about its center of curvature to acidetch the resist-free portion of the surface, and thereafter dissolving the remaining resist.

2. A method according to claim 1, including longitudinal shifting of said surface while said spray is directed thereagainst.

3. A method for providing a curved magnesium printing surface, comprising preforming a magnesium surface to the desired printing surface curvature, coating the surface with photo-sensitive poly-vinyl alcohol resist, exposing the coated surface to the image to be printed, developing the coating, directing against said surf-ace under positive pressure substantially radially thereof an etchant spray comprising a solution by weight of about 10.5-12.5

nitric acid, about 7% diethylbenzene, about 0.4% dioctyl sodium sulfosuccinate and about 0.3-1.5X10 gelatin while variably rotating the surface about its center of curvature to acid-etch the resist-free portion of the surface, and thereafter dissolving the remaining resist.

4. A method according to claim 3, including longitudinal shifting of said surface while said spray is directed thereagainst.

5. A method for providing a curved magnesium printing surface, comprising preforming a magnesium surface to the desired printing surface curvature, coating the surface with a photosensitive primary resist, exposing the coated surface to the image to be printed, developing the coating, coating the surface with a photosensitive secondary resist dissimilar to the primary resist, exposing the coated surface through a spread negative of the image to be printed in exact register with the first exposure, developing the secondary resist, directing an etchant spray against the surface under positive pressure substantially radially thereof while variably rotating the surface about its center of curvature to acid-etch the resist-free portion of the surface, dissolving the secondary resist by a solvent in which the primary resist is nonsoluble, directing an etchant spray against the surface substantially radially thereof while variably rotating the surface to further acid-etch the resist-free portion of the surface, and there-after dissolving the remaining resist.

6. A method according to claim 5, including longitudinal shifting of said surface while said sprays are directed thereag-ainst.

7. A method according to claim 6, in which said primary resist is polyvinyl alcohol, the secondary resist is photo-sensitized resin, the first-applied etchant is an aqueous solution of about 510% nitric acid, and the second-applied etchant comprises a solution by weight of about 10.5-12.5 nitric acid, about 7% diethylbenzene, about 0.4% di-octyl sodium sulfosuccinate and about 0.3-1.5 10- gelatin.

8. A method according to claim 7, in which each of said etchants is directed against said surface until an etch of about 0.020 inch depth is achieved.

9. A method according to claim 5, in which said primary resist in polyvinyl alcohol, the secondary resist is photo-sensitized resin, the first-applied etchant is an aqueous solution of about 510% nitric acid, and the second-applied etchant .comprises a solution by weight of about 10.5-12.5% nitric acid, about 7% diethylbenzene, about 0.4% di-octyl sodium sulfosuccina-te and about 0.3-1.5 10 gelatin.

10. A method according to claim 9, in which each of said etchants is directed against said surface until an etch of about 0.020 inch depth is achieved.

11. A method according to claim 5, in which each of said etchants is directed against said surface until an etch of about 0.020 inch depth is achieved.

12. A method of etching a curved metal printing plate having a predetermined radius of curvature and provided With a photoresist coating material which has been photographically exposed and developed, comprising the steps of rotating said printing plate about its longitudinal axis of curvature and simultaneously shifting said plate along said axis, and directing an etchant composition in the form of a spray comprising a plurality of liquid streams under positive pressure against said printing plate in a direction radially and normal to said axis of curvature for a period of time to etch the exposed metal surface of said printing plate to a desired depth without appreciable undercutting of relief areas in the printing plate.

13. A method of etching a curved metal printing plate having a predetermined radius of curvature and provided with a photoresist coating material which has been photographically exposed and developed, comprising the steps of rotating said printing plate about its longitudinal axis of curvature and simultaneously shifting said plate along said axis, and directing a spray comprising a plurality of aligned liquid streams of an etchant composition under positive pressure against said printing plate in a direction radially and normal to said axis of curvature for a period of time to etch the exposed metal surface of said printing plate to a desired depth without appreciable undercutting of relief areas in the printing plate.

14. A method of etching a curved magnesium printing plate as defined in claim 13, wherein the etching is continlliled to produce an etch depth of about 0.020 to 0.040 inc References Cited by the Examiner NORMAN G. TORCHIN, Primary Examiner.

MILTON STERMAN, HAROLD N. BURSTEIN,

Examiners. 

1. A METHOD FOR PROVIDING A CURVED METALLIC PRINTING SURFACE, COMPRISING PERFORMING A METALLIC SURFCE TO THE DESIRED PRINTING SURFACE CURVATURE, COATING THE SURFACE WITH A PHOTOSENSITIVE RESIST, EXPOSING THE COATED SURFACE TO THE IMAGE TO BE PRINTED, DEVELOPING THE COATING, DIRECTING AN ETCHANT SPRAY UNDER POSITIVE PRESSURE AGAINST THE SURFACE SUBSTANTAILLY THEREOF WHILE VARIABLY ROTATING THE SURFACE ABOUT ITS CENTER OF CURVATURE TO ACIDETCH THE RESIST-FREE PORTION OF THE SURFACE, AND THEREAFTER DISSOLVING THE REMAINING RESIST. 